1. Field of the Invention
This invention relates to a combined power transmission and electronic communication system and method of combining a power bus carrier and multiple communications signals. More particularly, the invention relates to multiple digital communication sources interconnected over power lines for communication thereamong thereby reducing cable weight and size in space applications, particularly satellites.
2. Description of the Prior Art
Because of the cost of launching satellites, techniques are required to minimize weight. Electrical cables used internally to distribute power and digital signals are a substantial portion of the total weight in space satellites. By combining the signal cables with the power cables, a weight savings can be realized. This is especially true in large command and control satellite systems.
The prior art discloses several examples of combined power and communications systems. In one example, U.S. Pat. No. 4,123,748, a burglar alarm system is described utilizing ultrasonic waves capacitively coupled as a signal on a DC power line. The capacitive coupling provides isolation but reduces the communication bandwidth of the system. In another example, U.S. Pat. No. 4,639,714, electrical power and communications signals are transmitted concurrently along a common electrical conductor. The electrical power signal is converted to a high frequency electrical power signal which is modulated as a function of the electrical communication signal. After the high frequency power signal is transmitted across an inductive coupler, the high frequency signal is converted to an appropriate DC or other electrical power signal and a communications signal. In still another example, U.S. Pat. No. 4,835,516, an audio frequency signal is capacitively coupled to a power line supply which limits the frequency bandwidth of the communication system. None of the prior art addresses the problem of weight and space for electrical power and communications systems in space applications. Either the combined power and communications systems are complicated, as in the '714 patent or they are bandwidth limited as in the '516 and '748 patents. The present invention, in contrast, provides an inductively coupled communications system and power transmission line which is not bandwidth limited and serves multiple digital sources, thereby reducing cable weight and space in a satellite.